Centrifugal pumps are used in a variety of applications. It is often desirable to recirculate fluid back to a centrifugal pump during intervals of low demand by an outlet device to prevent the pump from overheating. Overheating is caused by the exchange of heat between the running pump and stationary fluid present within the pump. Pump overheating lowers the vapor pressure resulting in fluid cavatation which can destroy the pump housing and impeller.
Recirculation valves are frequently used in centrifugal pumps to control overheating. One commonly used recirculation valve is a modulating flow control valve disclosed in U.S. Pat. No. 4,095,611. The valve disclosed in U.S. Pat. No. 4,095,611 has a circular disk-shaped check valve member interposed within a two-piece valve casing. During periods of normal downstream fluid demand, a pressure differential across the valve causes it to open and permit flow, while simultaneously blocking a fluid recirculation passageway. Conversely, during intervals of minimal downstream fluid demand, the disk-shaped check valve member returns to a closed position, thereby opening the fluid recirculation passageway and permitting fluid to recirculate back to the pump.
Another recirculation valve, disclosed in U.S. Pat. No. 4,243,064, has a circular main valve disk and bypass valve disk axially displaced among both ends of a connecting rod. During periods of normal fluid flow, the connecting rod moves to an open position causing fluid to flow out both the main outlet and the bypass outlet. When fluid flow is minimal, the bypass valve disk is superimposed over an annular seat which causes fluid to be redirected from the main outlet to the bypass outlet and recirculated through the centrifugal pump.
A problem encountered with the use of such recirculation valves is that they have complex structures, and are both costly to manufacture and difficult to maintain. Most of the recirculation valves presently available on the market, including the two described above, are constructed from two piece valve casings. A multiple piece casing is required because the valve members are too large to fit through the casing.
It is an object of the present invention to provide a recirculation valve having a one-piece valve casing and a multiple piece check valve member which can fit through and be assembled with the one piece casing and which regulates the flow of fluid from a centrifugal pump to a downstream device.
It is a further object of the present invention to provide a recirculation valve having a multiple piece valve member which can be easily inserted into and removed from a unitary valve housing.
It is an additional object of the present invention to provide a recirculation valve mechanism having a novel recirculation valve mechanism operated in association with the valve member so as to control the recirculation of fluid back to the centrifugal pump.